Although Ukraine had thousands of nuclear weapons stationed on its territory, these weapons did not really belong to Ukraine. Command and control is a core feature of an effective nuclear deterrent, but Kyiv did not have it. According to the official history written by the U.S. Defense Threat Reduction Agency, “The preplanned launch codes remained in the rocket army’s underground command and control centers…No one denied that authority to launch the nuclear forces, the third largest in the world, remained in Moscow.”
In other words, Russia retained effective command and control over the nuclear weapons on Ukrainian territory. Ukraine could not launch the missiles or use the warheads, and therefore the arsenal could not be used as a deterrent. Moreover, even if Ukraine did obtain command and control, it did not have the infrastructure to safely maintain the weapons.
Given these operational and technical limitations, the nuclear weapons in Ukrainian territory could simply not serve as an effective deterrent. They were, however, a valuable bargaining chip. Ukraine could not use the weapons, but it could trade them for other benefits.